Object AC (Aho-Corasick)

An Aho-Corasick multi pattern matcher created with T.ac( _pattern_array_ )

This is a convenience utility provided to you by the Trisul framework because multi pattern matching is such a frequent need in network analytics applications.

Creating the object

The object is created and stored in a global state, either as a global variable or as a member in the Global T table. Note that the global states are per-file not across LUA files.

onload = function()
	T.patternMatcher = T.ac( {'string1','string2','strin3'...})

.. later ..



A summary of the functions available in this object.

Name In Out Description
match_all string table Matches all patterns. The matches are returned in a table
{ pattern_matched = position }
The position indicates the last matching character, not the first.
match_one string table Same as match_all, but stops after finding a single match. Use this method for alerting on pattern matches.

Function match_all

Tries to match all patterns against the input text.


Use this parameter passed to your Lua function to integrate your data into the Trisul framework.


text string the text to be matched

Return value

A table of matches. See the debug output below


In this example we are attempting to match a list of hostnames against a DNS Full Text Search text.

The code at the point the dbg() is called is shown below

onload = function()
	T.patterns  = T.ac( { "toolbar", "nsatc",  "HOLLERITH" })

onflush= function(dbengine, fts)
	local m = T.patterns:match_all( fts:text() )
	if next(m)  then
		print("FOUND a match.. do your thing"

Using the debugger, we can inspect the return value m

debugger.lua> p m
m => {"toolbar" = 87}

debugger.lua> p fts:text()
fts:text() => "QUERY\9ID: 39219\9Flags:0×0100\9QDCount:1\9ANCount:0\9NSCount:0\9ARCount:0\


Function match_one

Match all the strings in the pattern against the input text.
Stop at the first match. The match_all tries to match all patterns and does not stop after the first match.